Photographic process

ABSTRACT

PHOTOGRAPHIC EMULSIONS DESENSITIZED WITH A DYE, HETEROCYCLIS COMPOUND OR HEAVY METAL SALT AREW RESENSITIZED WITH A TETRAZOLE, A TRIAZAINDENE, A TETRAZAINDENE, A PENTAZAINDENE, A PYRRIDINE OR A CYCLIC DISULFIDE.

United States Patent Ofice US. Cl. 96-101 17 Claims ABSTRACT OF THE DISCLOSURE Photographic emulsions desensitized with a dye, heterocyclic compound or heavy metal salt are resensitized with a tetrazole, a triazaiudene, a tetrazaindene, a pentazaindene, a pyrridine or a cyclic disulfide.

This invention relates to photographic processes, and more particularly to processes for resensitizing desensitized photographic silver halide emulsions.

Desensitized photographic silver halide emulsions which can be resensitized are useful in various applications, such as when the emulsion is handled in areas of high radiation prior to exposure. Thermal resensitization of desenitized photographic silver halide emulsions is described by Stewart and Reeves in US. Pat. 3,250,618, issued May 10, 1966. Such thermal resensitization provides highly useful results. However, in some instances it is desirable to effect resensitization at ambient temperatures. It therefore appears desirable to provide a technique for resensitizing desensitized photographic silver halide emulsions which does not require high temperatures.

One object of this invention is to provide a novel method for resensitizing desensitized photographic silver halide emulsions.

Another object of this invention is to provide a method for chemically resensitizing desensitized photographic silver halide emulsions.

Still another object of this invention is to provide a method for resensitizing desensitized photographic silver halide films whereby the resensitized photographic ,silver halide emulsion exhibits spectral sensitivity.

Other objects of this invention will be apparent from this disclosure and the appended claims.

These and other objectsof this invention are accomplished by contacting a desensitized photographic silver halide emulsion with a chemical resensitizing agent selected from the group consisting of the tetrazoles, the triazaindenes, the tetrazaindenes, the pentazaindenes, the pyridines and the cyclic disulfides. When a tetrazole or an azaindene is employed, it preferably contains a hydroxyl substituent. The following compounds are illustrative of the resensitizing agents useful in accordance with this invention:

Compound Resensitizing number: agent I 4-hydroxy-6-methyl 1,3,3'a,7 tetrazaindene. II S-thioctic acid. III 4-hydroxy-6 methyl-1,3a,7 triazaindene. IV -(3,4-dimethoxyphenyl)tetrazole. V 5-(4-cyanophenyl)tetrazole monohydene. VI a-Picoliniun1-fi-phenylethiodide. VII 4-hydroxy-6-methyl 1,2,3,3a,7-pentazaindene. VIII 6-hydroxy-4-methyl-1,2,3,3a,7 pentazaindene.

3,563,754 Patented Feb. 16, 1971 Compound Reseusitizing number: agent 1X u-Picolinic acid. X B-Picolinic acid. XI v-Picolinic acid. XII 2,4-dihydroxy 6 methyl-1,3a,-7-triazaindene. XIII 2,5-dimethyl-7 hydroxy 1,4,7a-triazaindene. XIV 5-amino-7-hydroxy-2-methyl 1,4,7a-

triazaindene. XV S-carboxy 4 hydroxy-1,3,3a,7-tetrazaindene. XVI l,2-bis(4-hydroxy 6 methyl-1,3,3a,

7-tetrazaindene -'5 -y1) ethane. XVII 1,2,3,4 tetrakis-(4-hydroxy-6-methyl 1,3,3a,7 tetrazaindene-Z-yl) butane XVIII 2-amini-5-carboxy-4 hydroxy 1,3,

3a,7-tetrazaindene. XIX 4-hydroxy- 2 -5 hydroxy ethyl-6- methyl-l,3,3a,7-tetrazaindene. XX 5-carbethoxy-4 hydroxy 1,3,3a,7-

tetrazaindine.

XXI 7-hydroxy-l,2,3,4,6 pentazaindene. XX II S-hydroxy 2'y hydroxypropyl 6- methyl-l,3,3a,7-tetrazaindene. XXIII 4-hydroxy-2(4 pyridyl) 6-1nethyl- 1,3,3a,7-tetrazaindene. XVIV 5-amino-2-(p carboxyphenyl)-7-hyhydroxy-l,3,4,6-pentazaindene. XXV Pyridine.

Other useful azaindenes are disclosed by the following references: Allen et al. US. Pat. No. 2,735,769, Feb. 21,

o 1956; Allen et al. US. Pat. No. 2,743,181, Apr. 24, 1956;

Tinker et al. US. Pat. No. 2,835,581, May 20, 1958; Reynolds US. Pat. No. 2,756,147, July 24, 1956; Carroll et al. US. Pat. No. 2,743,180, Apr. 24, 1956; Zeitschrift fur Wiss. Phot. 47, 2-28 (1952); Carroll et al. US. Pat. No. 2,716,062, Aug. 23, 1955; Allen et al. US. Pat. No. 2,772,164, Nov. 27, 195 6; Allen et al. US. Pat. No. 2,713,- 541, July 16, 1955; Tinker US. Pat. No. 2,853,375, Sept. 16, 1958; Carroll US Pat. No. 2,743,180, Apr. 24, 1956; Fry U.S. Pats. No. 2,566,6589, Sept. 4, 1951; Heimbach et al. US. Pats. No. 2,444,605-7, July 6, 1948 and Heimbach et al. US. Pats. No. 2,449,225-6, Sept. 14, 1948.

The useful pyridines include, in addition to pyridine, the picolines, the fi-lutidines, the a-lutidines, the 'y-collidines, the u,B-collidines, conyrine, the parvulines, the parvolines, ethylcollidine, coridine, rubidine and viridine.

' The useful pyridines may be hydroxy or carboxy substituted, e.g., the picolinic acids and 2- or 4-hydroxy pyridines are useful resensitizing agents.

As used herein, desensitized refers to photographic silver halide emulsions which are rendered substantially insensitive to the formation of latent images at radiations of wavelengths between about 1 and 1200 my Resensiti zations as used herein refers to increasing the response of desensitized emulsions to at least 10 times the desensitized speed to radiations of wavelengths between about 1 to 1200- III .0.

In accordance with the invention, resensitization can be accomplished by contacting the desensitized emulsion with the resensitizing agent in any convenient manner. Advantageously, a solvent for the resensitizing agent is present. For example, aqueous solutions of the resensitizing agent can be prepared. Most useful concentrations of resensitizing agent in such solutions is from about 1 gram to grams of resensitizing agent per liter of solution. The solution obtained can be spread over the desensitized 3 silver halide emulsion, or the desensitized emulsion can be dipped into the solution. The effective contact time to obtain resensitization varies depending upon the particular desensitizing agents and the resensitizing agents employed. Generally, residence times of 15 seconds to 10 minutes are effective to resensitize the emulsion.

Another highly useful method for contacting desensitized silver halide emulsions with resensitizing agents in accordance with the invention is to incorporate the resensitizing agent in a hydrophilic colloid, coat the mixture on a support, and bring the hydrophilic colloid layer containing resensitizing agent in contact with the desensitized photographic silver halide emulsion. Advantageously, the hydrophilic coating containing resensitizing agent is wet with water prior to contacting with the desensitized emulsion. Any suitable hydrophilic colloid can be used, such as gelatin, polyvinyl alcohol, hydrolyzed cellulose esters, albumins, and other hydrophilic colloids of the type described and referred to in Beavers US. Pat. 3,039,873, issued June 19, 1962, col. 13, lines 43-67. The hydrophilic colloid containing chemical resensitizing agent can be coated on any suitable support, such as cellulose acetate, polycarbonate, polyester such as polyethylene terephthalate and other types of photographic film supports, paper supports or plastic coated paper supports. The most useful concentration of resensitizing agent in hydrophilic colloid is about 10 mg. to 5 grams resensitizing agent per square foot. The coating of hydrophilic colloid containing resensitizing agent may be contacted with the desensitized photographic silver halide emulsion in any convenient manner, and for a time sufficiently long to effect resensitization. Most useful contact times are from about 10 seconds to about 10 minutes.

The photographic emulsions useful in practicing our invention comprise the conventional negative-type, developing out, unfogged photographic silver halide emulsions, such as silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chlorobromoiodide, and the like. The present emulsions generally have fog levels less than about .5 when developed for 5 minutes at 68 F. in Developer A which is described below. Also, the present emulsions, before desensitization, generally have sensitivities of at least about 3 log E, and preferably in the range of about to 1.5 log E, with satisfactory results being obtained with emulsions having sensitivities up to about 3 log E, E being the exposure in meter-candle-seconds required to produce a density of .2 above fog when developed for 5 minutes at 68 F. in Developer A. Developer A has the following composition:

Developer A: Grams N-methyl-p-aminophenol sulfate 2.2 Sodium sulfite, desiccated 72.0 Hydroquinone 8.8 Sodium carbonate, desiccated 130.0 Potassium bromide 4.0

Water to make one liter.

The silver halides can be dispersed in conventional photographic vehicles, such as gelatin, hydrolyzed polyvinyl esters, hydrolyzed cellulose esters, albumins, agar agar, gum arabic, etc. to form the present emulsions. Gelatin is preferred. The desensitized emulsions can be coated on any conventional photographic support or film, such as the supports referred to above.

Photographic silver halide emulsions which can be used in our invention also include photographic emulsions adapted for use in X-ray photography. It has been found that the latent image formation of such emulsions can be effectively inhibited and then treated according to the method of our invention to restore their sensitivity to X-rays.

The photographic silver halide emulsions according to our invention can contain a wide variety of the conventional chemical desensitizers that inhibit the ability of the emulsions to form latent images. The present photographic silver halide emulsions are made substantially insensitive to the formation of latent images with chemical desensitizers to radiations of at least about 1 to 1200 m and suitably within the wavelengths of gamma radiation and infrared radiation (i.e., about l 10 to 1X10 mu). Such treated emulsions can be exposed to X-ray radiation up to roentgens, and preferably up to 1000 roentgens, without having a density greater than .1 when developed for 5 minutes at 68 F. in Developer A, above. Some suitable chemical desensitizers are especially active and hence require only a few milligrams per mole of silver halide to decrease the emulsion photosensitivity by a large factor. Other chemical desensitizers, such as photographic spectral sensitizing dyes, are less efficient desensitizers and may require several grams in order to reduce effectively the photosensitivity of the silver halide emulsion to an extent sutficient to prevent fogging of the silver halide emulsion upon exposure to ambient radiation. Generally we utilize between about .01 to 5 grams of desensitizer per mole of silver halide in the emulsion. The optimum amount utilized for a particular desensitizer can be readily ascertained by one skilled in the art. Typical desensitizers which can be present in the photographic silver halide emulsions of our invention include heavy metal salts, such as mercury salts, rhodium salts, etc. Other chemical desensitizers which can be used in our invention comprise heterocyclic compounds containing at least one hetero sulfur and/or nitrogen atom. Heterocyclic desensitizers containing at least one benzene ring, and desirably containing at least one nitro substituent attached to the benzene ring, are especially useful. Typical of such organic desensitizers are benzotriazole compounds containing a nitro substituent on the benzene ring of the benzotriazole nucleus, e.g., 5-nitrobenzo 1,2,3-triazole, 4-nitrobenzo-1,2, 3-triazole, etc. (including their halogen substituted derivatives, such as 5-chloro-, 6-chloro-, etc.). Non-heterocyclic aromatic desensitizers containing at least one nitro substituent such as 3,5-dinitrobenzhydrazide and the like are also useful. Another group of chemical desensitizers comprise a class of dyes known as styryl dyes which contain at least one nitro substituent attached to a benzene ring. Other chemical desensitizers include anil and safranine dyes. Anthraquinone dyes containing a sulfoalkylaminosulfone radical can also be used to desensitize photographic silver halide emulsions useful in practicing our invention.

The following compounds are representative of other chemical desensitizers which are useful in treating photographic silver halide emulsions to inhibit their ability to form latent images.

DESENSITIZER 3,511initrobenzhydrazide 5-nitr0benzo-1,2,3,-triaz0le 4-nitro-G-chlorobcnzotriazole C-CHa 2,3-dimethyl-G-niltrobenzothiaZolium p-toluenesulfonate 2-pheny1benzo-'1, 2,B-lthiadiazolium bromide 63 GB N- -(CH2)m- N 0104 0104 N,N-decamethylene-bis (qu in'oxalinium) perchlona'te Methylene blue chloride 1-rnethyl-2 p-nitrosty ryl) (i-ethoxyquinolinium ptoluenesulfonate 2- (p-diethylaminophenyliminomethyl) -1,6-

dimethylquinolinium chloride G I OSOsC2 s C2115 :2 (pdimethylaminophenyliminolnethyl) 3- ethylbenzothi azolium ethosulfate cam 1 phenos afranine (chloride) NHz T pinakryp' tolgreen (chloride) NHz 1,3-di'zunino-5-methylphenazini-um chloride I CH3 3-melthyl-2-bis (phenylazo) methylene benzothi azoline anthraquinone-2-sulphotauride Patents which describe photographic silver halide desensitizers useful in treating the silver halide emulsions of our invention include the following, for example: Schuloff, US. 1,653,314, granted Dec. 20, 1927; Homolka, US. 1,760,756, granted May 27, 1930; Muller et al., US. 2,196,162, granted Apr. 2, 1940; Kendall et al., US. 2,541,472, granted Feb. 13, 1951; Kendall et al., US. 2,669,515, granted Feb. 16, 1954; Horwitz, US. 2,794,802, granted June 4, 1957; Groves, British 465,343, accepted Apr. 30, 1937; Compagnie, French 1,049,896, delivre Aug. 26, 1953; and addition, 64,756, delivre June 29, 1955; Compagnie, French 1,092,537, delivre Nov. 10, 1954. Compound 7 above Was prepared according to the method described by A. Burowoy, A. Chaudhuri and C. E. Vellins in Journal Chemical Society (London), page 90 (1956). Compound 11 is described by Mees- The Theory of the Photographic Process, 1st Ed., (Macmillan), page 1043 (page 422 of 2nd Ed) and by Kendall et a1., British Pat. 447,109, accepted May 4, 1936. Compound 16 can be prepared as described in French Pat. 1,049,896 (see French 1,092,537 for formula). Especially useful compounds which can be used as desensitizers include those represented by the following general formula:

wherein R represents an alcohol radical, i.e., a substituted or unsubstituted alkyl group, such as methyl, ethyl, propyl, butyl, ethoxycarbonylmethyl, fl-hydroxyethyl, carboxyalkyl, sulfoalkyl, etc.; R represents an aryl group, such as phenyl, or phenyl substituted by common organic radicals, such as hydroxyl, nitro, amino, alkylamino, dialkylamino, methyl, ethyl, ethoxyl, methoxyl, etc.; or,

R can represent a substituent having the formula:

(L=L)d-iCH=C(CH=CH)m-1l i-R wherein Z R and m are selected from the values given for Z, R and n, respectively; L represents a methine group, i.e., a --CR= group Where R represents a hydrogen atom or an alkyl group, such as methyl, ethyl, etc., X represents an acid radical, such as chloride, bromide, iodide, perchlorate, benzenesulfonate, p-toluenesulfonate, methylsulfate, ethylsulfate, etc., 11 and d each represents a positive integer of from 1 to 2, and Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing at least one sulfur and/or nitrogen atom and from 5 to 6 atoms in the heterocyclic ring, such nuclei being well-known to those skilled in the art. It is to be understood that the styryl dyes embraced by Formula A above preferably contain at least one benzene nucleus to which is attached at least one nitro group. Typical nuclei defined by Z include benzothiazole, quinoline, benzoxazole, indolenine, ,d-naphthothiazole, etc., which can contain simple substituents on the benzene ring thereof, such as methyl, ethyl, methoxyl, ethoxyl, hydroxyl, amino, etc. Other useful compounds which can be used as desensitizers are merocyanine dyes, such as those having the following general formula:

(C) "Z2 -Q\ RF-N(CH=CH) C(=L -L ,=-b=O wherein R Z L and 1 each represents a value selected from those given for R, Z, L and 11, respectively; p represents an integer of from 1 to 3; and, Q represents the atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms with the hetero atom being oxygen, nitrogen, sulfur or selenium, preferably, Q represents the atoms required to complete a S-membered nucleus containing 3 carbon atoms, 1 nitrogen atom and the remaining atom being either nitrogen, sulfur or oxygen.

The photographic silver halide emulsions of the invention can contain the usual emulsion addenda such as chemical sensitizers, antifoggants, plasticizers, hardeners, coating aids, and the like. Gold and sulfur sensitized emulsions are particularly useful. For example, the emulsions can be sensitized with sulfur, selenium or telluriurn compounds as described in Sheppard US. Pat. No. 1,574,- 944, Sheppard et al. US. Pat. No. 1,623,499, and Sheppard et al. US. Pat. No. 2,410,689. The emulsions are typically sensitized with gold salts as described in Waller et al. US. Pat. No. 2,399,083 and Damschroder et al. US. Pat. No 2,642,361. Suitable sensitizing gold compounds include potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2-aurosulfobenzothiazole methochloride.

It will be noted that useful heterocyclic desensitizers include the conventional photographic spectral sensitizing dyes which, when used at high concentrations desensitize photographic silver halide emulsions. Typical spectral sensitizing dyes which can be used in high concentrations to desensitize silver halide emulsions are those which contain the amidinium-ion chromophoric system, the carboxyl-ion chromophoric system or the amidic chromophoric system. For a description of these chromophoric systems, which are well known in the art, see Mees and James, The Theory of Photographic Process, third edition, published by the MacMillan Co., 1966, p. 201. Dyes having chromophoric systems include those of general formula B and C above. Typical general types of spectral sensitizing dyes which have such chromophoric systems include the cyanine, merocyanine, hemicyanine, p-dialkylaminostyryl, hemioxonol, holopolar and allopolar cyanine dyes. Specific dyes of this type are described by Mees and James, supra, all of which are useful, at high concentrations, as desensitizers. One advantage of using a spectral sensitizing dye (or combination of such dyes) as desensitizer is that after an emulsion desensitized therewith is resensitized in accordance with the invention, the silver halide emulsion exhibits spectral sensitivity in the region in which the dye absorbs. Hence, the same compound which is used as the desensitizer imparts the spectral sensitization upon emulsion resensitization. A group of highly useful spectral sensitizing dyes which can be used both as desensitizers and, upon resensitization, as spectral sensitizers, are listed below:

8 Identification letter: Dye

B 9-[1 (p dimethylaminophenyl)propen- 2-yl] 3,3 dimethylthiacarbocyanine bromide 3'-ethyl 3 methyl 9,11 neopentyleneoxathiadicarbocyanine iodide 1,1-diethyl-2,2'-carbocyanine iodide Anhydro 1 ethyl 1' (4-sulfobutyl)- 2,2-carbocyanine hydroxide 3,3 di [3 hydroxyethylthiadicarbocyanine bromide 9-ethyl 1',3 dimethylthia-Z'-carbocyanine iodide l-ethyl 2 [(3-ethyl-4-oxo 2 thioxo-S- thiazolidinylidene)ethylidene] 4 [(1, 3,3 trimethyl 2 indolinylidene)ethylidene]-3-phenyl-S-imidazolinone I Anhydro 3 ethyl 9 methyl-3-(3-sulfobutyl)-thiacarbocyanine hydroxide I Anhydro 9 ethyl 3 methyl-3-(3-sulfopropyl) 4,5;4,5 dibenzothiacarbocyanine hydroxide 5-[di(1 ethyl 2(1H) [3 naphthothiazolylidene) isopropylidenel 1,3 di(B- methoxyethyl)barbituric acid 9'-ethyl 3,3 dimethyl 4,5;4,5' dibenzothiacarbocyanine chloride 3,3'-diethyl 9 methylselenacarbocyanine bromide 4-(3,3 dicyanoallylidene) 1 ethyl-1,4-

dihydroquinoline 5,5 dichloro 3,3',9 triethylthiocarbocyanine bromide mm nmuo In some instances it is desirable to use combinations of non-spectral sensitizing desensitizers together with desensitizing concentrations of photographic spectral sensitizing dye. When such combinations are employed, spectral sensitivity is retained and in addition, the photographic emulsions exhibit the lowest fog for a given speed, or the highest relative speed for a given fog level.

This invention will be further illustrated by the following examples. Example 1 shows the resensitization of a desensitized photographic emulsion by treating with a solution of a tetrazaindene.

EXAMPLE 1 A photographic silver chlorobromide gelatin emulsion, sensitized with sulfur and gold sensitizers was split into two portions. To one portion was added a desensitizing concentration (1.5 grams per mole of silver) of the dye anhydro 3 ethyl-9-methyl-3'(3-sulfobutyl)thiacarbocyanine hydroxide. This dye is a spectral sensitizer at low concentrations. The emulsions were coated on a poly- (ethylene terephthalate) support at the rate of 300 mg. silver per sq. foot and 690 mg. gelatin per sq. foot. The coated films obtained were cut into several strips, and were treated, before exposure, for one minute With various concentrations of solutions of resensitizing agent in distilled water. The resensitizing agent, compound I, is identified above. The results obtained were compared to Identification films which had been given no resensitizing treatment, and letter: Dye which had been dipped in distilled water. The coatings A Anhydro 3 ethyl-9-methyl-3'-(3 sulwere exposed for 10 seconds on a sensitometer to light fobutyl) 4,5 benzothiacarbocyamne modulated by step tablet and were developed for five minhydroxide utes in Developer A above.

TABLE I Control Test Relative Relative Resensitizmg procedure speed 7 Fog speed 7 Fog 1. Control-n0 treatment 69 3. 9 07 1 05 2. Control-distilled water..." 5.5 .08 1 .05 3. 66.7 grams per liter Compound 209 3.8 .20 1, 000 3. S .17 4. 33.3 grams pm liter Compound I 214 4. (i 00 1, 000 3. U 0!! 5. 6.7 grams per liter Compound I 13S 5. (J 07 603 3. J 0G As used herein, means less than an means more than. It will be observed that in the above table, the test coatings exhibited an increase of speed more than 600"- fold when treated with a resensitizing agent in accordance with the invention.

The next example illustrates the process of resensitizing desensitized films using a web containing resensitizing agent in accordance with the invention.

EXAMPLE 2 The procedure of Example 1 was repeated except that instead of dipping the desensitized films in solution prior to exposure, the films Were resensitized by rolling in contact, for four minutes, with a poly(ethylene terephthalate) film having coated thereon 1.8 grams of gelatin per square foot and 45 mg. compound I per square foot. The web was dipped in water before contact with the desensitized emulsion. The test film was exposed and processed as described in Example 1. The results obtained were compared to control emulsion coating the same as in Example 1, which did not contain any desensitizer. The results are shown in Table 11.

TABLE II Relative speed 7 Fog A photographic gelatin silver chlorobromide emulsion, sensitized with sulfur and gold sensitizers, was prepared. The emulsion was split into several portions. One portion was coated on a support and served as a control. To three other portions of he emulsion were added various concentrations of the desensitizer 4-nitro-6-chlorobenzotriazole. All emulsions were coated on a poly(ethylene terephthalate) support at the rate of 137 mg. silver per square foot, 690 mg. gelatin per square foot. The three test coatings contained 1, 1.6 and 3 grams desensitizer per mole of silver. One set of each of these coatings was exposed and processed to provide a control. Another set of each of the coatings were bathed for one minute in a solution of distilled water containing 6.67 grams compound I per liter prior to exposure. The samples were exposed and processed as described in Example 1. The results obtained are described in Table III.

It will be seen in the above table that the resensitizing bath greatly increased the sensitivity of the emulsion which had been desensitized.

The following example shows the resensitization of desensitized films with a variety of resensitizing agents in accordance with the invention.

EXAMPLE 4 A test emulsion prepared as described in Example 1 was desensitized with 1 g. per mole of silver of the dye anhydro-3-ethyl-9-methyl 3 (3 sulfobutyl)thiacarbocyanine hydroxide. This emulsion was coated on a poly- (ethylene terephthalate) support at the coverages described in Example 1. The films obtained were treated with various solutions of resensitizing agents in accordance with the invention for various periods of time as shown in Table IV below. The films treated with solution of resensitizing agent compared to control films which were not bathed in anything prior to exposure and to a control that was bathed in water. Exposure and development were the same as in Example 1. An exposure was also made through a 1.5 neutral density filter together with a Wratten No. 16 filter (which is a yellow-colored filter) to give minus blue speeds. The results are shown in Table IV.

(In this table 1., refers to liter.)

TABLE IV Relative Concentration Time of minus Relative of resensitizing treatment, blue b He agent in water min. speed speed 7 Fog None 18 5 14 1 331 13 4. 8 13 5 741 23 9. 2 08 5 251 7. 1 6. 7 10 5 251 5. 5 3. 4 13 5 209 4. 8 4. 1 06 5 200 5. 0 4. 8 06 5 316 11. 2 5. 2 09 1 398 12. 6 3.8 07 10% pyridine 5 759 30 5. 3 22 10g. per 1. VII 5 3. 4 1. 6 07 10g. perl. VIII 5 417 10. 2 4. 3 07 1 Dmax. 0. 26. 2 DmuX-:0.25.

The effective resensitization of desensitized emulsions with a variety of agents is shown above. The unobvious nature of this invention is apparent since dye solvents, such as acetone and methanol, are completely ineffective in resensitizing such films.

The following example illustrates the resensitization of silver halide emulsions which have been desensitized with a high concentration of a variety of photographic spectral sensitizing dyes.

EXAMPLE 5 A photographic silver chlorobromide emulsion was prepared and coated on a poly(ethylene terephthalate) support at the rate of 300 mg. silver per square foot and 690 mg. gelatin per square foot. Various spectral sensitizing dyes were added in desensitizing concentration as shown in Table V. The coated films were resensitized and exposed for sec. on a sensitometer through a 1.5 new tral density filter, and developed for 5 min. in Developer A above. The coatings were resensitized by bathing in a solution containing 6.67 g. per liter of compound I for one minute before exposure. The sensitizing dyes employed are designated by letters, and are identified as above. The results obtained are shown in Table V.

TABLE V Resensitizing relative speed Dye (grams per mole silver) AAAA and J (.625) 25; and J (.625) and K (.063)

1 1 EXAMPLE 6 A photographic gelatin silver chlorobromide emulsion, sensitized with sulfur and gold sensitizers, was prepared. To this emulsion was added 625 mg. of dye I, 625 mg. of dye J and 63 mg. of dye K per mole of silver. Various concentrations of the desensitizer 2-phenyl-l,2,3-benzo thiazolium bromide were added to separate portions of that emulsion. Each emulsion obtained was coated on a poly(ethylene terephthalate) film support at a coverage of 137 mg. silver per square foot and 690 mg. gelatin per square foot. Several samples of each coating were given an overall exposure to 1,000 R. using 100 kv. X-rays. Each coating was then resensitized by placing it into contact with a web consisting of a polyester support having coated thereon a gelatin layer containing 1.8 g. of gelatin per square foot and 0.5 gram of compound I per square foot. Separate strips of this web were dipped in Water for 5 seconds, and then placed into contact with a sample of each coating for about 4 minutes at 70 F. Each emulsion coating was then exposed on an intensity scale sensitomer. Several samples of each coating were processed for various times ranging from 30 seconds to 3 minutes in a 3- pyrazolidone-ascorbic acid developer of the type described in US. Pat. 2,688,549. The films were fixed, washed and dried in the usual manner. The results obtained are shown in the following tables. Table VI shows the fog levels at different relative speeds. Table VII shows the relative speeds obtained for different fog values.

TABLE VI 2-pl|enyl-l,2,3- benzo thiadiazolium bromide Fog at a relative speed ol' (mg. per mole silver) 100 126 159 TABLE VII Relative Relative speed at; speed at a fog a fog of 0.25 of 0.5

EXAMPLE 7 A series of coatings was made and processed exactly as described in Example 6 above except that the emulsion contained only one desensitizing dye, 1 /2 g. of dye H per mole of silver. The results obtained are shown in Tables VIII and IX.

Example 8 demonstrates resensitization of a silver halide emulsion desensitized with a heavy metal salt in accordance with the process of the invention.

12 EXAMPLE 8 Treatment AExposed for M second on a sensitometer through a 1.5 neutral density filter.

Treatment B-As in A above but resensitized before eX- posure by bathing for 1 minute in a solution containing 6.67 gm. 4-hydroxy 6 methyl l,3,3a,7 tetrazaindene per liter.

Treatment C-As in B above but resensitizing solution contained 66.67 gms. of the tetrazaindene per liter.

The treated coatings were then developed for five minutes in developer A, above, fixed, washed and dried. The results obtained are shown in the following table.

TABLE X Treatment A Treatment B Treatment 0 Coneen- Rela- Rela- Relatration, tive tive tive lIgClz speed 7 Fog speed 7 Fog speed 7 Fog 2.8 1.30 .00 El. 7 3.20 ()6 14 3. 40 .06} 0.12 .10 5. 7 4. 20 (1(5 8. 7 3.51) 06 25 0. 26 15 4. 3 4. 0t) .12

l l)mnx. 2 No image.

EXAMPLE 9 The procedure of Example 8 was repeated except that instead of mercuric chloride the desensitizer used was 2 phenyl 1,2,3 benzothiadiazolium bromide, the test coating employing 0.6 g. of this desensitizer per mole of silver. This coating, together with a control which did not contain any desensitizer, was treated as follows:

Treatment AExposed for second on a sensitometer through a 1.5 neutral density filter, a No. 35 Wratten filter and a No. 38 Wratten filter.

Treatment B-As in A above but resensitized before exposure by dipping in 5% pyridine and then rolling in contact with the web described in Example 6 for one minute.

The exposed coatings are processed for 10 min. in a metol-hydroquinone developer having a ratio of 1 part metol to 4 parts hydroquinone. The results are shown in Table XI.

TABLE XI Treatment; A Treatment 13 Relative Relative speed 7 Fog speed 7 Fog 3.02 10 166 2. 7O .15 Dmnx------- 0.16 .12 2. 00 .12

The following example illustrates the effective desensitization achieved by using desensitizing concentrations of photographic spectral sensitizing dye.

EXAMPLE 10 ample 1. The results obtained are shown in the following table.

TABLE XII Dye per Relative mole silver speed '7 Fog The extent of the desensitization ofthese emulsions to X-ray radiation is shown in Table XIII below. The results shows in this table were obtained by exposing emulsions coated on polyester supports as described above. Exposure, however, was to 100-kv. X-rays, and development was in developer A, above. The developed densities obtained are shown in Table XIII below.

TABLE XIII 1 gram 1.5 gram X-ray level, dye per dye per roentgens No dye mole silver mole silver A photographic gelatin silver chlorobromide emulsion, containing sulfur and gold sensitizers, was desensitized with 4-nitro-6-chlorobenzotriazole held'at a concentration of 1.6 g. per mole of silver. The emulsion was split in several portions and some emulsions were spectrally sensitized with various sensitizing dyes. The sensitizing dyes were added at a low, conventional concentration for achieving spectral sensitization with minimum desensitization. This concentration was about 10 to mg. of dye per liter of emulsion. The dyes employed and the results obtained are indicated in Table XIV below. In obtaining these results, the emulsions were coated on poly- (ethylene terephthalate) films at a silver coverage of 137 mg. per square foot and a gelatin coverage of 202 mg. per square foot. The coated samples were exposed to 1000 R. using kv. X-rays, were developed for 5 minutes in Developer A above, and were fixed, washed and dried. The control coating was assigned an arbitrary relative speed of 100.

TABLE XIV Relative Density Feature speed at 1,000 R.

Control 100 0. 13 Control and dye L 1, 230 2.14: Control and dye M 1, 380 2. Control and dye D 680 1. 79 2, 040 2. 43

Control and dye O 780 2. 05

We claim:

1. A process for resensitizing a photographic element to record latent images, said element comprising a support having coated thereon a photographic negative-type, developing out, unfogged silver halide emulsion which has been rendered substantially insensitive to the formation of latent images at radiations of wavelengths between about 1 and 1200 mg by incorporation therein of a photographic silver halide emulsion chemical desensitizer selected from the group consisting of a heavy metal salt, an anthraquinone dye containing a sulfoalkylaminosulfone, radical, a non-heterocyclic aromatic compound containing at least one nitro radical, and a heterocyclic compound containing at least one hetero atom selected from the group consisting of a sulfur atom and a nitrogen atom, which comprises contacting said element with a resensitizing agent selected from the group consisting of the tetrazoles, the triazaindenes, the tetrazaindenes, the pentazaindenes, pyridine, a lower alkyl substituted pyridine, a carboxy substituted pyridine, a hydroxy substituted pyridine, and S-thioctic acid, for a period sufiicient to resensitize said emulsion to at least ten times the desensitized speed to radiations of wavelengths between about 1 and 1200 my.

2. A process for resensitizing photographic elements in accordance with claim 1 wherein said resensitizing agent is pyridine, a lower alkyl substituted pyridine, a carboxy substituted pyridine or a hydroxy substituted pyridine.

3. The process for resensitizing photographic elements in accordance with claim 1 wherein said heterocyclic compound is a photographic spectral sensitizing dye incorporated in said emulsion at a sufiiciently high concentration to render said emulsion substantially insensitive to the recording of latent images at radiations of wavelengths between 1 and about 1200 mg.

4. The process for resensitizing a photographic element in accordance with claim 3 wherein said photographic spectral sensitizing dye has a chromophoric system selected from the group consisting of the amidiniurn-ion system, the carboxyl-ion system and the amidic system.

5. The process for resensitizing a photographic element in accordance with claim 3 wherein said spectral sensitizing dye is selected from the group consisting of the cyanine, merocyanine, hemicyanine, p-dialkylaminostyryl, hemioxonol, holopolar cyanine, and allopolar cyanine dyes.

6. The process for resensitizing a photographic element in accordance with claim 3 wherein said photographic spectral sensitizing dye is anhydro-3-ethyl-9- methyl-3 3-sulfobutyl thiacarbocyanine hydroxide.

7. The process for resensitizing a photographic element to record latent images, said element comprising a support having coated thereon a photographic negativetype, developing out, unfogged silver halide emulsion rendered substantially insensitive to the formation of latent images at radiations of wavelengths between 1 and 1200 III/L by incorporation therein of anhydro-3-ethyl-9- methyl-3'-(3-sulfobutyl)thiacarbocyanine hydroxide at a concentration of 1.5 g. per mole of silver, which comprises bathing said element for about 5 minutes in an aqueous solution containing about 33 grams per liter of 4-hydroxy-6-methyl-1,3,3a,7-tetrazaindene.

8. The process for resensitizing a photographic element to record latent images, said element comprising a support having coated thereon a photographic negativetype, developing out, unfogged silver halide emulsion rendered substantially insensitive to the formation of latent images at radiations of wavelengths between 1 and 1200 m by incorporation therein of anhydro-3-ethyl-9- methyl-3'-(3-sulfo'butyl)thiacarbocyanine hydroxide at a concentration of 1.5 g. per mole of silver, which comprises contaeting said photographic element, for about 4 minutes, with a supported hydrophilic colloid coating wet with water and containing about 45 mg. per square foot of 4hydroxy-6-methyl-1,3,3a,7-tetrazaindene.

9. A process for resensitizing photographic elements in accordance with claim 1 wherein said resensitizing agent is a tetrazole.

10. A process for resensitizing photographic elements in accordance with claim 1 wherein said resensitizing agent is a hydroxy-substituted triazaindene.

11. A process for resensitizing photographic elements in accordance with claim 1 wherein said resensitizing agent is a hydroXy-substituted tetrazaindene.

12. A process for resensitizing photographic elements in accordance with claim 1 wherein said resensitizing agent is a hydroxy substituted pentazaindene.

13. A process for resensitizing photographic elements in accordance with claim 1 wherein said resensitizing agent is S-thioctic acid.

14. A process for resensitizing a photographic element to record latent images, said element comprising a support having coated thereon a photographic negative-type, developing out, unfogged silver halide emulsion which has been rendered substantially insensitive to the formation of latent images at radiations of wavelengths between about 1 and 1200 mg by incorporation therein of a photographic silver halide emulsion chemical desensitizer selected from the group consisting of a heavy metal salt, an anthraquinone dye containing a sulfoalkylaminosulfone radical, a non-heterocyclic aromatic compound containing at least one nitro radical, and a heterocyclic compound containing at least one hetero atom selected from the group consisting of a sulfur atom and a nitrogen atom, which comprises contacting said element with a resensitizing agent selected from the group consisting of 4 hydroxy 6 methyl 1,3,3a,7 tetrazaindene; 5-thioctic acid; 4-hydroxy-6-methyl-1,3a,7-triazaindene; 5-(3,4- dimethoxyphenyl tetrazole; 5 (4'-cyanophenyl tetrazole monohydrate; a-picolinium-fi-phenylethiodide; 4-hydroxy- G-methyl-l,2,3,3a,7-pentazaindene; G-hydroxy 4 methyll,2,3,3a,7-pentazaindene and pyridine.

15. A process for resensitizing a photographic element to record latent images, said element comprising a support having coated thereon a photographic negative-type, developing out, unfogged silver halide emulsion which has been rendered substantially insensitive to the formation of latent images at radiations of wavelengths between about 1 and 1200 m by incorporation therein of a photographic silver halide emulsion chemical desensitizer selected from the group consisting of a heavy metal salt,

an anthraquinone dye containing a sulfoalkylaminosulfone radical, a non-heterocyclic aromatic compound containing at least one nitro radical, and a heterocyclic compound containing at least one hetero atom selected from the group consisting of a sulfur atom and a nitrogen atom, which comprises exposing said desensitized element to radiation of wavelengths between about 1 and 1200 mg, and thereafter contacting said element with a resensitizing agent selected from the group consisting of 4 hydroxy 6 methyl 1,3,3a,7 tetrazaindene; S-thioctic acid; 4-hydroxy-6-methyl-1,3a,7-triazaindene; 5-(3,4- dimethoxyphenyl)tetrazole; 5 (4' cyanophenyl)tetrazole monohydrate; a-picolinium-fl-phenylethiodide; 4 hydroxy-6-methyl-1,2,3,3a,7 pentazaindene; 6 hydroxy- 4-methyl-1,2,3,3a,7-pentazaindene and pyridine.

16. A process for resensitizing photographic elements in accordance with claim 14 wherein said resensitizing agent is dissolved in aqueous solution at a concentration of about 1 to 100 grams resensitizing agent per liter of solution, and said solution is contacted with said photographic emulsion from about 15 seconds to 10 minutes.

17. The process for resensitizing photographic elements in accordance with claim 14 wherein said resensitizing agent is incorporated in a hydrophilic colloid and coated on a support, said resensitizing agent being incorporated in said colloid at a concentration of about 10 mg. to 5 g. per square foot, and said photographic emulsion is con tacted with said hydrophilic colloid coating for a time suflicient to resensitize said photographic emulsion.

References Cited UNITED STATES PATENTS 3,250,618 5/1966 Stewart et a1 9610l 3,352,672 11/1967 Hoppe 96101 3,411,914 11/1968 Oostes 96101 FOREIGN PATENTS 6,510,198 2/1966 Netherlands 96-101 NORMAN G. TORCHIN, Primary Examiner J. E. CALLAGHAN, Assistant Examiner US. Cl. X.R. 

